A conventional knife folding machine generally comprises a frame having a support surface to support a lower surface of a sheet, and a feed means attached to the frame to sequentially feed the sheet to a fold position on the support surface. The feed means comprises a drive roller and an idle roller which are parallel spaced from each other, and a conveyer belt extending between the drive roller and the idle roller. A part of the support surface is formed by a feed surface of the conveyer belt. A stopper is attached to the frame to position the sheet at the fold position by a front end of the sheet abutting the stopper.
The knife folding machine comprises a knife blade, a pair of folding rollers opposed to the knife blade at the folding position with the support surface therebetween; and a slider crank mechanism. The knife blade and the folding rollers extend in parallel to a feed path of the sheet. The slider crank mechanism reciprocates the knife blade between first and second positions via an opening through which the knife blade passes. The opening is formed on the support surface. The first position is opposite to the folding rollers with the support surface therebetween and spaced from the support surface. The second position is adjacent a gap between the folding rollers.
The knife blade has one end fixed to a rod which is connected with a crank of the slider crank mechanism. The crank makes one revolution every time the sheet is set at the fold position. During one revolution of the crank, the knife blade reciprocates between the first position (upper dead point) and the second position (lower dead point) so as to effect a folding operation. While the knife blade moves from the first position to the second position, the sheet on the support surface is folded in two by the knife blade, then an edge of the folded portion thereof is pushed out of the opening and inserted into the gap between the folding rollers so that the sheet can be folded by the folding rollers.
The conventional knife folding machine feeds the sheet to the fold position at a constant speed and sets the sheet at the fold position by a front end of the sheet abutting the stopper. It is preferable to feed the sheet at high-speed so as to increase a processing efficiency. However if the feed speed of the sheet becomes high, the sheet cannot be accurately set at the fold position because of the sheet rebounding from the stopper, and the sheet may be damaged or wrinkle by the sheet colliding with the stopper.
In order to solve the problems, in the conventional knife folding machine, a brush is attached opposite to the feed surface of the conveyer belt to contact the upper surface of the feed sheet to decelerate the sheet (see, for example, Patent Document 1), or a deceleration belt is arranged opposite to the conveyer belt to contact the upper surface of the sheet conveyed by the conveyer belt to decelerate the sheet (see, for example, Patent Document 2). The deceleration means disposed on the feed path of the sheet contacts the sheet to keep the speed of the sheet at a constant high-speed during feeding the sheet but reduce the speed of the sheet before the sheet abutting the stopper.
However these deceleration means decelerate the sheet conveyed by the conveyer belt by applying dynamic friction to the sheet and slipping the sheet on the feed surface of the conveyer belt. The deceleration means cannot always accurately stop the sheet at the fold position since it is difficult to control the position of the sheet on the way of decelerating. As a result, a position of the fold line on the sheet may be misaligned, which leads to the reduction of accuracy of the folding and a poor finish in the subsequent processes such as a sewing process and so on.
Patent Document 1: JP 2004-331402 A
Patent Document 2: JP 11-180635 A